net: use IS_ENABLED(CONFIG_IPV6)

Instead of testing defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/netns/xfrm.h b/include/net/netns/xfrm.h
index 748f91f..5299e69 100644
--- a/include/net/netns/xfrm.h
+++ b/include/net/netns/xfrm.h
@@ -56,7 +56,7 @@
 #endif
 
 	struct dst_ops		xfrm4_dst_ops;
-#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)
+#if IS_ENABLED(CONFIG_IPV6)
 	struct dst_ops		xfrm6_dst_ops;
 #endif
 };